Nim doesn't have interfaces. The amount of plumbing required to implement them is ridiculous. It has generics though. My point is how can recent OO languages miss this kind of stuff when designing their type system ? Crystal looks like a better bet, unfortunately it doesn't run on Windows.
At risk of sounding like a Go advocate when generics come up, the lack of interfaces doesn't bother me because interfaces themselves are a bit of a hack. When you have inheritance, object variants, generics, and a strong template/macro system, what's left for interfaces to do? I'd much rather have all of these other things than interfaces alone.
The fact that you can create an online interface and an unrelated library (which you didn't write) can have structures that implement your interface automatically is pretty useful (and cool) IMHO.
Fair point, but much of that benefit is lost without decent support for those third-party implementations to be loaded dynamically. So Nim is missing one piece, but those other features I mentioned can get you very close to the same place. Go is missing the other piece, with no really good way to make up for it. That problem's not even solvable as long as Go's runtime makes no provision for interfacing to code that doesn't play by its own (ever-changing, undocumented) rules about things like goroutines and GC. I know which shortcoming I'd rather live with.
